Muscle Physiology (Section 4)

A single muscle contraction and relaxation cycle produced by a single action potential is called a _____.

The time interval between the generation of a muscle-fiber action potential and the onset of mechanical contraction is known as the _____ period.

When two or more muscle twitches combine from rapid repetitive stimulation to produce greater total tension, the phenomenon is called _____.

A smooth, fused, maximal muscle contraction produced by high-frequency stimulation with no relaxation between stimuli is called _____.

Inability of a muscle to maintain target tension despite continued neural stimulation is termed muscle _____.

Accumulation of lactic acid and extracellular _____ ions are metabolic contributors to peripheral muscle fatigue.

Subjective tiredness caused by alterations within the central nervous system rather than at the muscle fiber level is called _____ fatigue.

In an _____ contraction, muscle tension remains constant while the muscle shortens and moves a load.

In an _____ contraction, the muscle develops force without changing its overall length or moving a load.

Non-contractile connective tissues and tendons that must be pulled tight before muscle tension is transmitted to bone are called _____ components.

The relationship between sarcomere length, actin-myosin overlap, and isometric tension generation is described by the _____ relationship.

Somatic motor neurons that directly innervate skeletal muscle fibers have their cell bodies located in the _____ horn of spinal-cord gray matter.

All human somatic motor neurons release the neurotransmitter _____, which exerts an excitatory effect at the neuromuscular junction.

A single somatic motor neuron and all the individual muscle fibers it innervates constitute a _____.

When a somatic motor neuron fires an action potential, all muscle fibers within that motor unit contract in an _____ manner.

Fine motor control, such as in extraocular eye muscles, is provided by _____ motor units.

Large motor units, such as those in the _____ muscle, are adapted for producing powerful, gross contractions.

Increasing total muscle force by activating additional and larger motor units is called motor-unit _____.

Skeletal muscle organizational hierarchy proceeds from whole muscle to fascicles, muscle fibers, myofibrils, and finally _____.

The functional, repeating contractile unit of a myofibril bounded by two Z discs (lines) is a _____.

In sarcomere banding, the dark band containing thick myosin filaments and overlapping thin actin filaments is the _____ band.

The light band of a sarcomere that contains only thin actin filaments anchored to Z discs is the _____ band.

The central lighter region within the A band containing only thick filaments is the _____ zone.

The structural line located at the center of the H zone that anchors thick myosin filaments is the _____ line.

During muscle contraction, thin actin filaments slide over thick myosin filaments toward the center of the _____.

During sarcomere shortening, the length of the A band remains constant, whereas the lengths of the I band and _____ zone decrease.

At the neuromuscular junction, acetylcholine binds to _____ receptors on the specialized motor end plate.

ACh binding at the motor end plate produces graded depolarizations called _____ potentials (EPPs).

Action potentials propagate deep into the interior of the muscle fiber through invaginations of the sarcolemma called _____.

Depolarization of T tubules triggers the release of _____ ions from the terminal cisternae of the sarcoplasmic reticulum (SR).

Released calcium ions bind to _____, causing a conformational change that shifts tropomyosin away from actin-binding sites.

In relaxed muscle, the protein _____ physically blocks the myosin-binding sites on thin actin filaments.

Myosin heads possess _____ enzyme activity, enabling them to hydrolyze ATP into ADP and inorganic phosphate (Pᵢ).

During the cross-bridge power stroke, the release of ADP and _____ causes the myosin head to tilt and pull the actin filament.

Binding of a new molecule of _____ to the myosin head is required for myosin to detach from the actin filament.

Depletion of ATP after death prevents myosin detachment, resulting in a state of muscular rigidity known as _____.

Muscle relaxation requires active transport of Ca²⁺ back into the sarcoplasmic reticulum by _____ pumps.

Massive, explosive release of acetylcholine at the neuromuscular junction is caused by _____ spider toxin.

Inhibition of ACh release via prevention of synaptic vesicle exocytosis is caused by _____ toxin.

The plant alkaloid _____ acts as a competitive antagonist, blocking nicotinic ACh receptors at the motor end plate.

Chemicals that inhibit the enzyme _____ increase ACh concentration in the synaptic cleft, prolonging muscle stimulation.